telescope

an optical instrument for making distant objects appear larger and therefore nearer. One of the two principal forms (refracting telescope) consists essentially of an objective lens set into one end of a tube and an adjustable eyepiece or combination of lenses set into the other end of a tube that slides into the first and through which the enlarged object is viewed directly; the other form (reflecting telescope) has a concave mirror that gathers light from the object and focuses it into an adjustable eyepiece or combination of lenses through which the reflection of the object is enlarged and viewed.Compare radio telescope.

1640s, from Italian telescopio (used by Galileo, 1611), and Modern Latin telescopium (used by Kepler, 1613), both from Greek teleskopos "far-seeing," from tele- "far" (see tele-) + -skopos "seeing" (see -scope). Said to have been coined by Prince Cesi, founder and head of the Roman Academy of the Lincei (Galileo was a member). Used in English in Latin form from 1619.

v.

"to force together one inside the other" (like the sliding tubes of some telescopes), 1867, from telescope (n.). Related: Telescoped; telescoping.

telescope

[tĕl′ĭ-skōp′]

An arrangement of lenses, mirrors, or both that collects visible light, allowing direct observation or photographic recording of distant objects.♦ A refracting telescope uses lenses to focus light to produce a magnified image. Compound lenses are used to avoid distortions such as spherical and chromatic aberrations.♦ A reflecting telescope uses mirrors to view celestial objects at high levels of magnification. Most large optical telescopes are reflecting telescopes because very large mirrors, which are necessary to maximize the amount of light received by the telescope, are easier to build than very large lenses.

Any of various devices, such as a radio telescope, used to detect and observe distant objects by collecting radiation other than visible light.

telescope

A device used by astronomers to magnify images or collect more light from distant objects by gathering and concentrating radiation. The most familiar kind of telescope is the optical telescope, which collects radiation in the form of visible light. It may work by reflection, with a bowl-shaped mirror at its base, or by refraction, with a system of lenses. Other kinds of telescopes collect other kinds of radiation; there are radio telescopes (which collect radio waves), x-ray telescopes, and infrared telescopes. Radio and optical telescopes may be situated on the Earth, since the Earth's atmosphere allows light and radio waves through but absorbs radiation from several other regions of the electromagnetic spectrum. X-ray telescopes are placed in space.